CENTRAL MASS. — It's being called the strongest flu season in years, and it has hit Massachusetts earlier than usual — at a time when fewer people have been vaccinated.

“Getting vaccinated is the single most effective way to protect against the flu,” Massachusetts Department of Public Health interim Commissioner Dr. Lauren Smith said. “The good news is flu vaccines are widely available, and it’s absolutely not too late to get a flu shot in order to protect yourself and your loved ones.”

The federal Centers for Disease Control and Prevention reported widespread flu in 47 states in a Friday report, up from 41 the week before. In Massachusetts, there have been more than 6,000 laboratory confirmed cases of flu, with participating health care providers indicating that more than 4 percent of all office visits consist of patients reporting flu symptoms.

The Massachusetts Department of Public Health has distributed more than 760,000 doses of pediatric and adult flu vaccine to clinical providers and public sites, including local boards of health, community health centers, Visiting Nurse Associations and homeless shelters. It is working with local boards of health to offer additional public flu clinics in anticipation of expanded demand.

“This year’s flu vaccine has shown to be a particularly effective match against the dominant strains of influenza currently circulating, and vaccine supplies are ample,” Smith said.

Nationally, the CDC said 3,000 to 49,000 influenza deaths are estimated to occur each year, varying with the severity of the season.

Besides getting vaccinated, individuals can take other steps to prevent the spread of flu. These include frequent hand washing with soap and warm water, covering a cough or sneeze with a sleeve rather than the hands, and staying home from work or school if sick.